Production of poly(ethylene terephthalate)

ABSTRACT

Disclosed herein is a novel crystalline form of low molecular weight poly(ethylene terephthalate). This crystalline form may be produced from molten or glassy low molecular weight poly(ethylene terephthalate) material by means of rapid heat transfer to or from the material. The poly(ethylene terephtalate) composition is suitable for use as a starting material for solid-state polymerization in order to produce polymers of higher molecular weight.

FIELD OF THE INVENTION

This invention concerns a process for obtaining a novel form of lowmolecular weight poly(ethylene terephthalate) and its use in solid-statepolymerization to obtain a higher molecular weight polymer.

TECHNICAL BACKGROUND

Poly(ethylene terephthalate), herein abbreviated PET, is widely used inmany materials and products, such as fibers, fabrics, molding resins,and soda bottles. Most of these uses require a polymer of relativelyhigh molecular weight. Such polymers have been commercially made byraising, either in melt or solid-state polymerization, the molecularweight of a prepolymer or oligomer.

Melt polymerizations require higher temperatures, which is more likelyto cause polymer decomposition, and expensive equipment. Solid-statepolymerizations, in contrast, are usually run at somewhat lowertemperatures. Solid-state polymerizations also have the advantage,compared to melt polymerizations, that very high molecular weights,where melt viscosities would otherwise be extremely high, can be morereadily obtained. In commercial use, however, solid-statepolymerizations may be relatively slow. Furthermore, solid-statepolymerizations usually require that the lower molecular weight PET, inthe form of particles or pellets, undergo a relatively lengthycrystallization process prior to being polymerized in the solid-state.Therefore, better polymerization methods for PET are desired.

N. S. Murthy, et al., Polymer, vol. 31, p. 996-1002; C. M. Roland,Polym. Eng. Sci., vol. 31, p. 849-854; and A. Siegman, et al., J. Polym.Sci., Polym. Phys. Ed., vol. 18, p. 2181-2196 (1980) all report on theproperties, particularly the crystalline properties, of various PETpolymers. None of these polymers disclose or teach the novel form ofPET, and their associated properties, claimed herein.

U.S. Pat. Nos. 3,405,098, 3,544,525, 4,064,112, 4,165,420, 4,254,253,and 4,271,287, and F. Pilati in G. Allen, et al., Ed., ComprehensivePolymer Science, Vol. 5, p. 201-216 (Pergamon Press, Oxford 1989)describe various aspects of solid-state polymerization and/or thepreparation of PET for use in solid-state polymerization. None of thesepatents or references discloses the novel processes or compositions ofthe present invention.

SUMMARY OF THE INVENTION

This invention concerns a composition, comprising, poly(ethyleneterephthalate) having a degree of polymerization of about 5 to about 35,an average crystallite size of 9 nm or more, and a melting point of 270°C. or less.

This invention also concerns a process for crystallizing poly(ethyleneterephthalate), comprising, cooling at a rate sufficient to cool amolten poly(ethylene terephthalate) or, alternatively, heating at a ratesufficient to heat a glassy poly(ethylene terephthalate) particle to atemperature of about 120° C. to about 210° C. This process produces acrystalline poly(ethylene terephthalate) having an average crystallitesize of 9 nm or more and a melting point of 270° C. or less and apoly(ethylene terephthalate) having a degree of polymerization of about5 to about 35. By "degree of polymerization" is meant a statisticalaverage, since such polymeric molecules usually have a distribution ofmolecular weights.

More particularly, disclosed herein is a process for the crystallizationof pellets of poly(ethylene terephthalate), comprising:

heating pellets of a glassy poly(ethylene terephthalate) pellet to abulk average temperature of 120° C. to about 210° C. within specifiedmaximum period of time and, furthermore, maintaining the pellets at thatbulk average temperature for a specified minimum period of time; or

cooling molten droplets (meaning small portions) of a poly(ethyleneterephthalate) so that the bulk average temperature of the droplets orcrystallizing pellets is brought to a temperature of 120° C. to about210° C. within a specified maximum period of time and, furthermore,maintaining the crystallizing pellets at that bulk average temperaturefor a specified minimum period of time;

provided that said poly(ethylene terephthalate) has a degree ofpolymerization of about 5 to about 35.

This invention also concerns a process for the solid-statepolymerization of poly(ethylene terephthalate), wherein the improvementcomprises, starting with a poly(ethylene terephtalate) having an averagecrystallite size of 9 nm or more, a melting point of 270° C. or less,and a degree of polymerization of about 5 to about 35.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative X-ray diffraction pattern of a sample of a PETpolymer according to the present invention.

FIG. 2 is another illustrative X-ray diffraction pattern of a sample ofa PET polymer according to the present invention.

FIG. 3 is an illustrative X-ray diffraction pattern of a sample of a PETpolymer according to the present invention, which pattern has beendeconvoluted into two overlapping Gaussian peaks.

DETAILS OF THE INVENTION

A novel composition of poly(ethylene terepthalate), also referred to asPET, is disclosed herein. This novel composition is characterized by acertain kind of crystalline morphology and other desirablecharacteristics. Related characteristics are also disclosed. By PET orpoly(ethylene terephthalate) herein is meant poly(ethyleneterephthalate) which may be modified with small amounts, less than 10mole percent, and more preferably less than 5 mole percent of thepolymer repeat units, of copolymerized monomers (or "co-repeat units"),so long as the crystallization behavior of the polyester issubstantially the same as "homopolymer" PET.

The present PET has an average crystallite size of about 9 nm or more,preferably 10 nm or more, more preferably about 12 nm or more, andespecially preferably about 14 nm or more. The average crystallite sizeis measured by wide angle X-ray powder diffraction, the method orprocedure for which is as follows.

PET samples of uniform thickness for X-ray measurements are produced bycryogrinding the PET in a SPEX™ Freezer/Mill (Metuchen, N.J.) underliquid nitrogen for 30 seconds and then compressing the PET into disksapproximately 1 mm thick and 32 mm in diameter. Because of the fragilenature of some of the PET disks, all disks are mounted on standardsample holders using 3M Scotch™ double-sided sticky tape. Consequently,it is necessary to collect powder diffraction patterns of the PET disks(+tape) and a tape control. While it is preferable that the sample'spatterns are collected over the range 15°-19° 2θ (as shown in FIG. 2),the patterns of the samples (+tape) and a tape control can be collectedover the range 10°-35° 2θ in some cases, as was obtained for some of thesamples (as shown in FIG. 1). The diffraction data are collected usingan automated Philips diffractometer operating in the transmission mode(CuKα radiation, curved diffracted beam monochrometer, fixed step mode(0.05°/step), 65 sec./step, 1° slits, sample rotating). Aftersubtracting the powder diffraction pattern for the tape control issubtracted from each of the sample-plus-tape (sample+tape) diffractionpatterns, Lorentz-polarization corrections are applied to each powderpattern.

To remove the local background scattering from the 15°-19° 2θ region ofeach powder pattern, a straight line extending from 15.00° to 19.00° 2θis defined and subtracted. This region of the diffraction pattern hasbeen found to contain two crystalline reflections, at approximately16.5° and 17.8° 2θ, that have been defined as the (011) and (010)reflections, referred to by N. S. Murthy, et al., in Polymer, vol. 31,p. 996-1002, herein incorporated by reference.

FIGS. 1 and 2 show the diffraction patterns, corrected as detailedabove, collected over the 2θ range 10°-35° and 15°-19°, respectively. Inaddition to the Miller indices of the reflections of interest, the local"artificial" background between 15° and 19° 2θ, labeled "b", anddescribed above, is shown.

The 15°-19° region is then deconvoluted into two overlapping Gaussianpeaks corresponding to the two crystalline reflections, and theposition, width, and height of both peaks are extracted. An example ofthis deconvolution is shown in FIG. 3. The apparent crystallite size forthe (010) reflection (herein sometimes also referred to simply asapparent crystallite size), ACS₀₁₀, is calculated from the reflection'sposition and full width at half height using the Scherrer equation, asfor instance described by L. E. Alexander, X-Ray Diffraction Methods inPolymer Science, p. 335 et seq. (John Wiley & Sons, N.Y., 1969):##EQU1## where ACS₀₁₀ is the mean dimension of the crystal, K is assumedto be 1.0, λ is the wavelength, β is the full width at half height ofthe profile, in radians, and θ has its normal meaning.

The PET has a melting point (T_(m)) of 270° C. or less, preferably 265°C. or less, and more preferably between 200° C. and 265° C., dependingon the DP. The melting point is measured by Differential ScanningCalorimetry (DSC). The T_(m) is taken as the maximum of the meltingendotherm on the first heat. In contrast, samples of conventional PETwhich have been highly annealed (annealed over long periods) samples ofPET, although they may have large crystallite sizes, also have highmelting points, above 270° C.

It is also preferred if the PET has no distinct premelting endotherm. Bya "premelting endotherm" is meant an endothermic peak in the DSC due toa melting endotherm at a lower temperature than (before) the mainmelting endotherm. By "distinct" is meant the melting occurs over atemperature range of 60° C. or less, preferably less than 40° C. Byhaving "no distinct premelting endotherm" is meant that if one or moresuch endotherms are detected, the total heat of fusion is less than 1J/g, preferably less than 0.5 J/g. Premelting endotherms are believed tobe indicative of small and/or relatively imperfect crystallites, andwhen present, the PET particle may have a tendency to more readily stickto other particles when heated, usually at or around the temperature ofa premelting endotherm, which is very undesirable in solid-statepolymerization.

The PET of the present invention also has a degree of polymerization(DP) of about 5 to about 35, preferably about 10 to about 25. The DP ismerely the average number of repeat units in a polymer chain and,therefore, may not necessarily be an integer. The main repeat unit ofPET is ##STR1## The DP can be determined by Gel PermeationChromatography using appropriate PET standards.

The DP is merely one way of expressing the molecular weight of the PET.Another comparable measure of molecular weight is the intrinsicviscosity (IV) of the polymer. Listed below for the convenience of thereader are the IVs of PET polymers and their approximate DP's. Thesenumbers assume that the ratio of the weight average molecularweight/number average molecular weight for the PET is "normal" for acondensation polymerization, about 2-3. The relationship between DP andIV is approximately DP=155.5(IV)¹.466.

    ______________________________________            DP   IV    ______________________________________            5    0.10             9.6 0.15            11.6 0.17            12.6 0.18            15.8 0.21            16.9 0.22            19.2 0.24            35   0.36    ______________________________________

The PET of the present invention may be made by rapidly heating glassyPET to a certain temperature range or by cooling molten PET to that sametemperature range. The PET can be in the form of particles or pellets ofvarious size and shapes or mixtures thereof, as will be readilyappreciated by the skilled artisan. By a "glassy PET" is meant a PETbelow its T_(g) which contains less than about 10 weight percentcrystalline PET, preferably less than about 5 percent, most preferablylesss than 1 weight percent. The amount of crystalline PET present canbe determined by standard methods using DSC to determine the heat offusion of the crystallites present and comparing that with the heat offusion of "pure" crystalline PET. By a "molten PET" is meant a PET inthe liquid (not glassy) state. Preferably it contains less than tenpercent (10%), more preferably less than five percent (5%), and mostpreferably less than one percent (1.0%) crystalline PET. It is preferredif the initial temperature of the molten PET is about 255° C. or higher,preferably about 270° C. or higher, since this is approximately at orabove the common melting point of PET. In order to obtain a largeapparent crystallite size, it is preferred to have as littlecrystallinity in the starting PET as possible.

It has been found that the desired PET crystalline morphology may beformed by rapidly heating or cooling amorphous PET to a preselectedtemperature range. A temperature range of 120° C. to about 210° C.,preferably about 150° C. to about 190° C., has been found to produce thedesired result.

Accordingly, in this process, not only must a temperature gradient beimposed between the PET and its surroundings, but heat (or anotherappropriate form of energy) should be removed or added to the polymer ata relatively high rate. If heating, conductive and/or radiant heat asobtained in conventional ovens may be employed. For example, ovens inwhich heat flows primarily by radiation and/or conduction, from thesurroundings, into the PET material or particle may be employed.Preferably, the heat radiation has a frequency below microwave, e.g.,below 15 megaherz.

This requires that the surroundings or environment of the PET be able totransfer this heat rapidly. Preferably, the cross-sectional area of thePET should not be so large that the change of temperature of the PET isrelatively rapid on the surface but inadequate or too slow in thecenter.

When crystallizing from molten PET, then in order to obtain rapid heattransfer into the molten PET, it is preferred if the PET is in goodcontact with a heat-transfer material that has a relatively high overallheat capacity (derived from both its mass and its actual heat capacity)and thermal conductance. Metals are particularly useful for thispurpose, especially metals with high coefficients of heat transfer.However, coated metals, plastics and other materials may be employed fortransfering heat to molten PET during crystallization.

The surface of the molten PET may be exposed to a combination of heattransfer materials, for example, a part of the surface may be exposed toa metal surface and another part of the surface may be exposed to, forexample, a gas. Although a gas may be used to transfer heat to or fromthe PET, the heat capacities of gases are relatively low, and so suchcooling would be more difficult to achieve by itself. Liquids at theappropriate temperature may also be used, but they may be less preferredbecause of concerns that contamination may occur and because of the needto separate the liquid from the PET. Thus, it is preferred to at leastpartially cool the molten PET by contact with a heat conductive solid.

Conversely, when starting with glassy PET instead of molten PET, theglassy PET should be rapidly heated instead of cooled. One way toaccomplish this is expose the glassy PET to a very high temperatureenvironment, about 300° C. to 800° C. or higher for up to about 120seconds. See Examples 1 and 5 for examples of such a procedure.Generally speaking, the higher the temperature or the smaller the crosssection of the PET being treated, the less time that will be needed. Informing the desired crystalline form of PET by heating or cooling, it ispreferred that the entire crystallization process, i.e., heating orcooling and crystal formation, be complete in less than 5 min, morepreferably less than 120 sec, more preferably less than 90 sec, and mostpreferably preferably about 3 to about 60 sec. When crystallizing moltenPET, the particles may be be maintained at the temperature ofcrystallization for longer periods of time. When crystallizing glassyPET, however, prolonged exposure to the temperature of crystallizationmay be detrimental to the desired result.

As mentioned above, the minimum cross section of the PET, usually in theform of particles or pellets, is important in determining how fast thebulk of the PET is heated or cooled. Generally speaking, it is preferredif the maximum cross section, or its average value, for the PET which isto be heated or cooled is about 1 cm or less, more preferably about 0.6cm or less. Preferably, the minimum cross section, or its average, is500 nm.

The shape of the crystallized PET may vary, and may be a film, ribbon,particles of various shapes, etc. In one preferred embodiment, the PETis in the form of particles (or, more accurately, small discrete units,masses, or droplets in the case of molten PET). Crystalline PET in theform of particles is particularly useful in solid-state polymerization.Preferred forms and/or sizes for particles are spherical particles withdiameters of 0.05 mm to 0.3 mm, hemispherical particles with a maximumcross section of 0.1 mm to 0.6 mm, or right circular cylinders with adiameter of 0.05 mm to 0.3 mm and a length of 0.1 cm to 0.6 cm. Ifshapes such as films or ribbons are formed, then if desired, they can belater ground, cut, or otherwise divided into particles, such as aresuitable for solid-state polymerization. Since it is preferred if thepellets are produced on an economically advantageous commercial scale,the pellets would preferably be produced and collected together incommercial quantities of greater than 10 kg, more preferably greaterthan 50 kg. The pellets may be used in the same plant soon after beingmade, stored for later use, or packaged for transport, all in commercialquantities.

Before reaching a stable shape, molten or crystallizing PET may beaffected by the shape of the means into which it can flow or withinwhich it is confined before solidification, whether such means employsphysical or other forces.

Glassy PET, for use as a starting material in a crystallizaton processaccording to a method of the present invention, may be made by veryrapidly cooling the appropriate molecular weight molten PET to below theglass transition temperature of PET. This can be done in bulk or whileforming particles of the PET. The PET itself can be made fromappropriate methods known to the artisan, see for instance B. Elvers, etal., Ed., Ullmann's Encyclopedia of Industrial Chemistry, vol. A21, p.232-237 (VCH Verlagsgesellschaft mbH, Weinheim, 1992). Such a glassypolymer may be stored or shipped (preferably in a relatively dry state)for later polymerization to higher molecular weight, whether asolid-state polymerization, melt polymerization, or other processing.

In all of the processes described herein for the crystallization of lowmolecular weight PET to form crystallites with relatively large apparentcrystallise sizes, it is preferred that the heating or cooling, asdesired, takes places in less than 120 sec., more preferably about 90sec., and most preferably about 3 to 60 sec.

In an integrated plant for producing PET from monomeric materials, lowmolecular weight PET will usually be available as a molten material.Thus, it is preferred if the instant process starts with molten PET,which is then cooled. It is convenient, and therefore preferred, if thePET is formed in "particles" just before or essentially simultaneouswith the cooling of the molten PET to form the desired crystallinemorphology. The preferred eventual sizes and shapes of such particlesare as given above.

The molten PET may be formed into particles (or, if molten, perhaps moreaccurately portions of PET) by a variety of methods, includingpastillation (see copending commonly assigned concurrently filedapplication U.S. Ser. No. 08/376,599 (CR-9623); U.S. Ser. No. 08/375,873(docket no. CR-9638), and U.S. Ser. No. 08/376,596, (docket no.CR-9524), all three applications hereby incorporated by reference intheir entirety, or U.S. Pat. No. 5,340,509, prilling as desribed innumerous patents such as U.S. Pat. No. 4,165,420, melt cutting, dripping(see Example 2 below), or extruding (see Example 3 below). Aprilling/degassing device for polymers is available from SouthwestResearch Institute (Dallas, Tex.). The PET portions or particles can beconveniently cooled by contacting them with a metal surface, preferablyin a controlled temperature environment, such as a conveyor belt ormoving table held at the proper temperature to achieve the desiredcrystalline morphology. It is preferred if the PET initially contactsthis metal while still largely molten, since this contact with a liquidwill usually lead to better heat transfer. A regulated flow of an inertgas may be passed over the particles to increase the overall rate ofcooling.

In an integrated process for producing high molecular weight PET, thelow molecular weight PET having the morphology described above may befurther polymerized to higher molecular weight. The PET may be meltedand melt polymerized, but the crystalline PET described herein isespecially suitable for use in solid-state polymerization. Solid-statepolymerization is well known to the artisan. See, for instance, F.Pilati in G. Allen, et al., Ed., Comprehensive Polyer Science, vol. 5,p. 201-216 (Pergamon Press, Oxford 1989), which is hereby incorporatedby reference. Solid-state polymerization is particularly useful formaking higher molecular weight PETs. In general, particles of PET areheated to a temperature below the melting point and a dry gas, usuallynitrogen, is passed, usually concurrently in continuous operation,around and over the particles. At the elevated temperature,transesterification and polycondensation reactions proceed, and the gascan be employed to carry away the volatile products (similar othermethods, such as employing a vacuum, may be used for this purpose),thereby driving the PET molecular weight higher.

In the past, a number of problems or difficulties have been associatedwith the solid-state polymerization of PET. In particular, the particlesto be polymerized usually have had to undergo an annealing process, sothat when they are heated during solid-state polymerization, they do notundergo partial melting and stick together. If, alternatively, thepolymerization occurs at a relatively lower temperature to avoidsticking, this would increase the polymerization time, since thereactions which drive the molecular weight up proceed faster at highertemperatures. In either event, these difficulties or problems tend tomake the solid-state polymerization process more expensive to run.

Advantageously and surprisingly, the PET polymer with the crystallinemorphology disclosed herein may be directly polymerized (preferablywithout further crystallization or annealing) starting at highertemperatures, for instance 230° C., preferably 240° C. The need for alengthy annealing step, which lengthens the overall process time isthereby avoided. In addition, particles produced according to thepresent process may, in some cases at least, be more resistant toattrition. This would usually be advantageous where PET particles, insolid-state polymerization apparatus, tend to wear against each other orthe apparatus itself. Thus, the use of the particles produced accordingto the present invention can result in an improved process forsolid-state polymerization.

In any polymerization of low molecular weight PET to higher molecularweight PET, normal additives, such as polymerization catalysts, may bepresent. These may have been added when the low molecular weight PET wasformed. A typical catalyst is Sb₂ O₃, whose concentration herein isgiven as the level of elemental antimony. Because of the higher startingpolymerization temperatures in solid state polymerization using thecrystalline low molecular weight PET, as described herein, it may bepossible to use lower catalyst levels while maintaining usefulpolymerization rates. Lower catalyst levels may be advantageous when thePET is intended for use in making certain products, for example, whenthe PET is intended for use in making bottles which will store beveragesfor human consumption.

In the following Examples, certain analytical procedures are used. Asidefrom X-ray diffraction, which is described in detail above, theseprocedures are described below. References herein to these types ofanalyses, or their results, correspond to these exemplary procedures.

Intrinsic Viscosity (IV)

A solvent is made by mixing one volume of trifluoroacetic acid and threevolumes of methylene chloride. PET, in the amount of 0.050 g, is thenweighed into a clean dry vial, and 10 mL of the solvent is added to itusing a volumetric pipette. The vial is closed (to prevent evaporationof the solvent) and shaken for 30 min or until the PET is dissolved. Thesolution is poured into the large tube of a #50 Cannon-Fenske™viscometer, which is placed in a 25° C. water bath and allowed toequilibrate to that temperature. The drop times between the upper andlower marks are then measured in triplicate, and should agree within 0.4sec. A similar measurement is made in the viscometer for the solventalone. The IV is then calculated by the equation: ##EQU2##

Gel Permeation Chromatography (GPC)

GPC was run in a Waters™ 150C ALC/GPC instrument, using as a solventhexafluoroisopropanol (HFIP) containing 1.3637 g of sodiumtrifluoroacetate per L. The instrument was run in the usual way, andstandard calculations were made to determine M_(n) (number averagemolecular weight) and M_(w) (weight average molecular weight).Calibration of the instrument was made using a PET sample with M_(n)22,800 and M_(w) 50,100.

Melting Point

Melting point was determined by Differential Scanning Calorimetry (DSC)and all samples were analyzed using a TA Instruments™ DSC 910. Theinstrument was calibrated with indium consistent with the systemdocumentation. The samples were analyzed as received, no pre-grinding,using 5-10 mg ±0.005 mg. The samples were sealed in aluminum pans thenheated from room temperature to 300° C. at 10° C./min. in a nitrogenpurged environment. Glass transition temperature, melting pointtemperature and heat of fusion calculations were done with the TAInstrument software. The reported DSC peak melting temperature is thecorresponding temperature of the peak in the main melting endotherm.

Thermomechanical Analysis

A Mettler™ TMA 40 Analyzer coupled to a TSC 10A controller was used forall samples. This instrument was calibrated for temperature using thestandard operating procedure illustrated in the instruction manual at 1month intervals or when spurious results were suspected. The samples hadno extra pre-treatment in the TMA system that would alter the samplesinherent morphological history. The partial hemispherical particles wereloaded in the system in contact with both the quartz sample holder and a3 mm diameter probe such that the sample was convex side up with theprobe in contact with the apex of the hemisphere. Two temperatureprofiles were used to analyze the samples. The first being a high speedscanning rate of 10° C./min. from room temperature through the melt andthe second, to ensure a homogeneous heat envirnoment, being a 1° C. ratefrom 200° C. to the melt.

In the Examples, SSP means solid-state polymerization.

EXAMPLE 1

PET with an IV of 0.18 dl/g and COOH ends of 167.5 Eq/10⁶ g was producedby a melt-phase polymerization process and contained approximately 275ppm Sb as a catalyst. The melt was then extruded through a 1 mm diameterorifice to form droplets. The droplets fell through an air gap of about10 cm into chilled water to form clear amorphous particles. Theparticles were shaped like pancakes, approximately 8 mm in diameter and2.2 mm thick. The particles were crystallized one at a time in aMettler™ TMA 40 coupled to a Mettler™ Thermal Controller 10A. Theindividual particle was placed on top of the quartz sample holder atroom temperature. The oven was preheated to 400° C., lowered over thesample for 15 seconds, then removed allowing the particle to cool backto room temperature. After exposure in the oven the particle was opaque.DSC analysis of the crystallized sample indicated no pre-meltingendotherms. The peak melting temperature was 250.1° C. The ACS₀₁₀ was11.6 nm.

EXAMPLE 2

PET with an IV of 0.15 dl/g, and COOH ends of 188.2 Eq/10⁶ g, which hadbeen produced by a melt-phase polymerization process and which containedapproximately 275 ppm Sb as a catalyst, was heated in a Melt Indexer at290° C. until the polymer dripped out of the orifice (1 mm in diameter)under its own weight. A hot plate covered with a 1.9 cm thick steelplate was placed 15 to 25 cm under orifice of the melt indexer. Thetemperature was monitored by a thin-wire thermocouple kept in intimatecontact with the steel plate. The polymer dripped onto the hot steelplate which was at 180° C. Crystallization was monitored by observingthe clear amorphous drop turn into an opaque solid. Once it was opaquethe metal surface was tipped at an angle to horizontal so the particlewould slide off and cool to room temperature. The particles were shapedlike pancakes, approximately 5.6 mm in diameter. DSC analysis of thecrystallized sample indicated no pre-melting endotherms. The peakmelting temperature was 250.3° C. Two particles formed by this methodwere placed one on top of the other in a quartz sample holder in a TMAand a load of 0.5N was applied on them with the probe. The particlesshowed no signs of adhesion after being held for 30 minutes at 240° C.under this load.

PET with an IV of 0.24 dl/g and COOH ends of 27.8 Eq/10⁶ g, which hadbeen produced by a melt-phase polymerization process and which containedapproximately 275 ppm Sb as a catalyst, was heated in a Melt Indexer at290° C. until the polymer dripped out of the orifice (1 mm in diameter)under its own weight. A hot plate covered with a 1.9 cm thick steelplate was placed 15 to 25 cm under the melt indexer. The temperature wasmonitored by a thin-wire thermocouple kept in intimate contact with thesteel plate. The polymer dripped onto the hot steel plate which was at180° C. Crystallization was monitored by observing the clear amorphousdrop turn into an opaque solid. Once it was opaque the metal surface wastipped at an angle to horizontal so the particle would slide off andcool to room temperature. The particles were shaped like hemispheres,approximately 4.5 mm in diameter and 2.5 mm thick. DSC analysis of thecrystallized sample indicated no pre-melting endotherms. The peakmelting temperature was 258.7° C. Two particles formed by this methodwere placed one on top of the other in a quartz sample holder in the TMAand a load of 0.5N was applied on them with the probe. The particlesshowed no signs of adhesion after being held for 30 minutes at 240° C.under this load.

EXAMPLE 3

PET with an IV of 0.21 dl/g and COOH ends of 141.0 Eq/10⁶ g, which hadbeen produced by a melt-phase polymerization process and which containedapproximately 275 ppm Sb as a catalyst, was melted and processed at255°-280° C. through a 16 mm twin screw extruder at 0.5 lb/hr. The meltextruded through a 1.0 mm die forming individual droplets that fell 1.3cm through room temperature air onto a heated turntable. The turntableprovided precise regulation of surface temperature and residence time onthe heated surface, with continuous particle formation from theextruder. The device consisted of a rotary actuator driven by a steppermotor, a rotating stainless steel turntable in contact with a stationaryheated plate. The temperature of the turntable surface was controlledthrough manipulation of the temperature of the stationary plate. Acalibration curve was generated for the controlled measured temperatureof the stationary plate versus the surface temperature of the turntableso that a thermocouple did not have to be attached to the rotatingturntable during the crystallization. After about 300° of rotation onthe turntable the crystallized particles hit a block of Teflon®fluoropolymer which knocked them off the turntable and into a roomtemperature collection pail. For particles formed at surfacetemperatures between 160°-200° C. there were no premelting endotherms inthe DSC traces. Processing conditions and particle analyses are listedin Table I.

                  TABLE I    ______________________________________                       Time      DSC Peak            Table Temp on Table  Melting Temp                                           ACS.sub.010    Run No. (°C.)                       (sec)     (°C.)                                           (nm)    ______________________________________    1       160        28        255.4     12.5    2       160        23        254.1      9.8    3       170        23        255.5     10.9    4       170        45        255.5     10.0    5       190        45        253.1     12.0    6       190        28        254.8     12.5    7       200        45        254.4     13.8    8       200        60        254.2     12.6    ______________________________________

EXAMPLE 4

PET with an IV of 0.17 dl/g and COOH ends of 98.0 Eq/10⁶ g, which hadbeen produced by a melt-phase polymerization process and which containedapproximately 275 ppm Sb as a catalyst, was melted and processed througha Prism 16 mm twin screw extruder and dropped onto a heated turntable asdescribed in Example 3. Processing conditions and particle analyses arelisted in Table II.

                  TABLE II    ______________________________________                                DSC Peak           Turntable  Time on   Melting           Temperature                      Turntable Temperature                                         ACS.sub.∩1∩    Run No.           (°C.)                      (sec)     (°C.)                                         (nm)    ______________________________________    1      120        10        251.9    11.3    2      120        28        251.9    11.7    3      120        60        251.5    11.4    4      160        28        251.8    13.6    5      160        60        251.9    16.2    6      170        28        252.6    13.4    7      200        60        252.3    15.2    ______________________________________

EXAMPLE 5

PET with an IV of 0.18 dl/g and COOH ends of 132.1 Eq/10⁶ g, which wasproduced by a melt-phase polymerization process and which containedapproximately 275 ppm Sb as a catalyst, was prilled to form clearamorphous particles. About 100 g of particles were placed on a piece ofKapton® polyimide film (3 mil thick) which was placed on a roomtemperature ceramic plate. The particles, film and plate were thenplaced in a Fisher Scientific model 497 high temperature oven for 15seconds at 500° C. The particles were removed from the oven and allowedto cool to room temperature. The oven dimensions were 30.5 cm×30.5cm×35.6 cm and the ceramic plate was placed in the center of the oven.The crystallized particles showed no premelting endotherms in the DSCtrace. Fifty grams of particles were loaded into a glass tube (5.1 cmD×40.6 cm H) that was surrounded by a larger diameter glass tube. Acontrolled volumetric flow rate and temperature of nitrogen passedthrough a porous disk distributor at the bottom of the column and thenthrough the 5.1 cm D reactor. Heated air passed through the outsideglass tube to insulate the reactor from heat loss. When necessary toprovide particle motion, as when conventional crystallization wasoccurring, an agitator shaft with three propeller blades at variousheights within the column was slowly rotated.

    ______________________________________    Program for 0.18 IV, TSC, SSP @ 210° C.    Duration           N.sub.2 Flow                    Air Flow N.sub.2 Temp                                    Air Temp    (min)  (1/min)  (1/min)  (°C.)                                    (°C.)                                            Agitator    ______________________________________    15     200      150      25 to 210                                    25 to 210                                            on    1440    40      150      210    210     off    15     200      150      210 to 25                                    210 to 25                                            off    ______________________________________

Samples were taken at 0, 6 and 24 hours for analysis:

    ______________________________________    Analysis of 0.18 Particles TSC, SSP @ 210° C.                       DSC Peak    Time   IV          Melting Temperature                                      ACS.sub.010    (hr)   (dl/gm)     (°C.)   (nm)    ______________________________________    0      0.18        254.5          10.7    6      0.19        263.5          --    24     0.46        267.8          13.5    ______________________________________

50 gm of the TSC particles were also solid state polymerized at 240° C.under the following conditions:

    ______________________________________    Program for 0.18 IV, TSC, SSP @ 240° C.    Duration           N.sub.2 Flow                    Air Flow N.sub.2 Temp                                    Air Temp    (min)  (1/min)  (1/min)  (°C.)                                    (°C.)                                            Agitator    ______________________________________    15     200      150      25 to 240                                    25 to 240                                            on    1440    40      150      240    240     off    15     200      150      240 to 25                                    240 to 25                                            off    ______________________________________

Samples were taken at 0, 6 and 24 hours for analysis:

    ______________________________________    Analysis of 0.18 Particles TSC, SSP @ 240° C.                       DSC Peak    Time   IV          Melting Temperature                                      ACS.sub.010    (hr)   (dl/gm)     (°C.)   (nm)    ______________________________________    0      0.18        254.5          10.7    6      0.53        --             --    24     1.14        282.0          12.2    ______________________________________

About 50 g of the same amorphous material were crystallized for 16 h at90° C. DSC of this material showed a small crystallization peak at 117°C. that extended to the main melting endotherm, indicating that theparticles were still partially amorphous. The main melting peak was at255.5° C. This material was further crystallized and solid statepolymerized at 210° C. under the following conditions:

    ______________________________________    Program for 0.18 IV, Conventionally Crystallized, SSP @ 210° C.    Duration           N.sub.2 Flow                    Air Flow N.sub.2 Temp                                    Air Temp    (min)  (1/min)  (1/min)  (°C.)                                    (°C.)                                            Agitator    ______________________________________    60     200      150      25 to 210                                    25 to 210                                            on    60     200      150      210    210     on    1440    40      150      210    210     off    15     200      150      210 to 25                                    210 to 25                                            off    ______________________________________

Samples were taken at 0, 6 and 24 hours for analysis.

    ______________________________________    Analysis of 0.18 Particles Conventionally Crystallized,    SSP @ 210° C.                    DSC Peak    Time IV         Melting Temperature                                   ACS.sub.010    (hr) (dl/gm)    (°C.)   (nm)    ______________________________________    0    0.18       255.5          too amorphous    6    0.22       251.8          --    24   0.20       261.7          8.8, 8.5    ______________________________________

What is claimed is:
 1. A composition, comprising, modified or unmodifiedpoly(ethylene terephthalate) having a degree of polymerization of about5 to about 35, an average apparent crystallite size of 9 nm or more, anda melting point of 270° C. or less.
 2. The composition as recited inclaim 1 wherein said average apparent crystallite size is about 12 nm ormore.
 3. The composition as recited in claim 1 wherein said averageapparent crystallite size is about 14 nm or more.
 4. The composition asrecited in claim 1 wherein said melting point is 265° C. or less.
 5. Thecomposition as recited in claim 1 wherein said degree of polymerizationis about 10 to about
 25. 6. The composition as recited in claim 5wherein said average apparent crystallite size is about 12 nm or more,and said melting point is 265° C. or less.
 7. The composition as recitedin claim 1 wherein said modified poly (ethylene terepthalate) comprisesup to 5 mol percent of comonomers other than ethylene terepthalaterepeat units.
 8. The composition as recited in claim 1 wherein saidmodified poly (ethylene terephthalate) comprises comonomers selectedfrom the group consisting of isophthalic acid, triethylene glycol,1,4-cyclohexane dimethanol, 2,6-napthalene dicarboxylic acid, adipicacid, esters of the foregoing, diethylene glycol, and mixtures thereof.9. Particles of the composition of claim
 1. 10. Particles of modified orunmodified poly(ethylene terepthalate) having a degree of polymerizationof about 5 to about 35, an average apparent crystallite size of 9 nm ormore, and a melting point of 270° C. or less.
 11. The particles as inclaim 10 having having an average apparent diameter of 500 micrometersto 2 cm.
 12. The particles as recited in claim 10 or 11 wherein saidaverage apparent crystallite size is about 12 nm or more.
 13. Theparticles as recited in claim 10 or 11 wherein said average apparentcrystallite size is about 14 nm or more.
 14. The particles as recited inclaim 10 or 11 wherein said melting point is about 265° C. or less. 15.The particles as recited in claim 10, 11 or 12 consisting essentially ofparticles in an amount over 10 kg.
 16. The particles as recited in claim10 or 11 wherein said degree of polymerization is about 10 to about 25.17. The particles as recited in claim 10 or 11, wherein the particlesare spherical, semi-spherical, cyclindrical, or pancake-like in shape.